A number of procedures have been developed for treating superficial lesions, such as, for example, warts, on human and animal skin. Lesions can be removed, for example, through the localized freezing of the skin lesion tissue by a cooling fluid, such as a liquid refrigerant. Physicians have used liquid nitrogen applications, for example, to freeze and remove lesions from a patient's skin. Conventional methods of treatment, however, may have the disadvantages of requiring specialized equipment to condense the nitrogen gas, the need for specialized storage devices, and the inherent hazards of handling and dispensing materials having very low boiling points, for example, as low as approximately −196° C. in the case of liquid nitrogen.
More recently, various methods have been developed to treat skin lesions cryosurgically by employing a cooling fluid (e.g., a cryogenic fluid) contained, for example, in a handheld pressurized container. Such cryosurgical devices generally rely upon a liquefied (compressed) gas, such as, for example, butane, propane, or dimethyl ether (DME), to rapidly cool an applicator tip or “bud” based on the principles of “heat of vaporization.” In other words, as the compressed gas flows to and contacts a surface of an applicator, such as, for example, a porous applicator bud, rapid evaporation of the gas causes the applicator surface to cool to temperatures which are lower than the temperature of the liquefied gas alone. In several such methods, an effective amount of the cryogenic fluid from the pressurized container can be dispensed, for example, into a hollow supply tube having a cotton, fiber and/or plastic foam bud located at the distal end of the supply tube. The cryogenic fluid accumulates in the applicator and upon evaporation, cools the applicator to temperatures well below freezing. The applicator can be placed in contact with the skin surface of the lesion for a period of time sufficient to reduce the temperature of the skin lesion tissue to temperatures that freeze the skin, such that permanent, irreversible rupture of the cellular membranes of the tissue occurs.
Cryosurgical devices currently utilizing the heat of vaporization principal in combination with compressed gases, such as DME for example, can pose various issues. For example, the devices can depend significantly upon the particular gas used and rates of evaporation from the applicator may be relatively long (e.g., on the order of 15-30 seconds). Moreover, the effective temperature of the applicator (i.e., the temperature of the applicator that is sufficient to cause freezing of the skin lesion) may be reached for only a short period of time, particularly once placed in contact with the warmer surface of the skin lesion, thereby limiting effective freezing of the target tissue.
Various additional cryosurgical devices can utilize liquid nitrogen, or other liquefied gases such as, for example, chlorofluoro carbons or nitrous oxide, which have significantly lower boiling points and thus can be dispensed at colder temperatures than some conventional “heat of vaporization” gases such as DME, thereby achieving more aggressive freezing effects. Such cryosurgical devices, however, are generally still relatively complex in their structure, using complicated valving mechanisms and dispensers to deliver the liquefied gas. Accordingly, problems can arise with such devices due to the high pressures exhibited by the gases the complicated manner in which the cryogenic fluid is moved from the container to the dispensing tip, the ease of use, and/or the cost associated with manufacture and/or assembly of the devices.
Accordingly, it may be desirable to provide a cryosurgical device that is both simple in terms of structure and use, and capable of delivering a variety of cryogenic fluids, including more aggressive cooling agents, such as, for example, nitrous oxide and liquid nitrogen, in an amount sufficient to achieve effective cryosurgical treatment. It may be further desirable to provide a disposable cryosurgical device that can be discarded once spent. It may, therefore, be desirable to provide an economical device with simpler structural components and flow regulation mechanisms, which can also reduce waste of the cryogenic fluid as it is moved from a container, for example to an applicator, for dispensing at a desired location.